1/ which graph illustrates constant speed and velocity

a) a
b) b
c) c
d) d

2/ ice / water / steam
as matter changes state from gas to liquid, which of these statements is true ? ?

a) the particles speed up.

b) the particles slow down.

c) the particles get farther apart.

d) the attractive force between the particles decreases.

best answer gets

Velocity is said to be constant if its magnitude as well direction at any instant is remains the same. In D, if you draw a line parallel to y-axis at any time t, you can see that velocity is same. Hence, D is the correct graph.

The kinetic energy of gaseous molecules is greater than that of liquid molecules. Therefore, in gas, kinetic energy overcomes the force of attraction between molecules. In short, in gas phase, particles move at high speed and hence they have less force of attraction. In case of liquid phase, particles are close enough as a result there is much more force of attraction compared to gaseous molecules. In liquid state, kinetic energy cannot overcome force of attraction therefore, liquid molecules slow down.

Therefore, B is the correct answer.